Mr. Podesta, who served as Chief of Staff in former President Bill Clinton's second term, would likely take on the role of a campaign manager, according to reports, sending signals about Clinton's nascent campaign.

After serving under Mr. Clinton, he founded the Center for American Progress, a liberal think tank in Washington, DC. The Obama administration brought him on as a special counselor to the President about a year ago to help reinvigorate Mr. Obama's political fortunes.

Podesta has counseled Obama in both foreign and domestic policy, advising him on matters including Ebola, immigration, and climate change. He was the surprise force behind negotiations with the Chinese government aimed at reducing greenhouse-gas emissions.

For starters, if it weren't already obvious, it's another unmistakable sign that Clinton is running.

"The move is one of the most definitive signs yet that Mrs. Clinton is building the apparatus to launch a 2016 run," writes the Wall Street Journal.

It's also a sign that Clinton has learned from her mistakes from her 2008 bid, when a lack of staff unity and discipline cost her the nomination.

Podesta would likely serve as a strategist and troubleshooter for Clinton, working to "stave off the sort of internal staff feuding that erupted in Mrs. Clinton’s failed 2008 presidential bid," reports the Journal.

The Independent calls his likely role "enforcer of discipline...something that was famously missing during her tumultuous bid in 2008..."

And by calling on Podesta, Clinton is making it clear that's she's serious.

Podesta is the guy people call on when the going gets tough: He served as Bill Clinton's chief of staff from 1998 to 2001, helping control a series of crises including Clinton's impeachment trial. The Obama administration brought him on to help the President steer a path through Congressional impasses and to avert embarrassments like the Affordable Care Act's botched rollout.

When it comes to hiring, managing, and overseeing a staff, Podesta is known as a master.

"[H]e has given as much thought to the form and function of the White House staff as anyone in the Democratic Party. Probably more," writes Politico.

And as the architect of the liberal Center for American Progress, Podesta is both well-connected with other party intellectuals and well-versed in Democratic policy ideals, giving him "a deep reservoir of credibility within Democratic circles," adds Politico.

Of course, he's also a close friend and longtime political ally of the Clintons. In addition to serving as Bill Clinton's chief of staff, he has held a top role in the family's charitable foundation.

Bill Clinton, for one, has nothing but praise for Podesta.

As he once told the WSJ about his former chief of staff, “He’s very straight forward. He doesn’t play games with people. You always know where he stands."

And with her Podesta hire, Clinton is also making clear where she stands in 2016.